The present invention relates to generally an electrostatic ink-jet printer and more particularly an ink-drop-landing-position control electrode disposed adjacent to the back of a recording medium so as to ensure the deposition of ink drops at their correct destinations.
In order to improve the qualities of images printed by the ink-jet printer, the particle size of ink drops must be reduced as practically as possible. However an ink drop with an extremely fine diameter cannot have kinetic energy sufficient to overcome aerodynamic and electrostatic disturbances while it is in flight. As a result, it is considerably deflected from an intended trajectory and consequently deposited at an unpredictable position, resulting in distortion of the printed image.
In order to attain a high printing speed, in the electrostatic ink-jet printers, a recording paper is in general transported in the direction perpendicular to the traveling path of a print head. That is, the recording medium is drawn upward while the print head moves transversely across the recording medium. A pair of deflection plates of the print head are arranged upright and in parallel with each other. As a result, when a line of ink dots is drawn in the horizontal direction, the firstly placed ink dot has been advanced upward by a distance depending upon the feed velocity of the recording medium from the position at which the last ink drop lands. That is, each ink drop is placed at a position lower than those of the preceding ones. As a result, the line of dots thus formed is inclined at an angle with respect to the horizontal. In the case of a multi-nozzle ink-jet print head, each line segment drawn by each nozzle is inclined so that the resulting line of dots has the form of sawteeth.